Current lithium-ion batteries, or cells, use a solid reductant as the anode and a solid oxidant as the cathode. Solid-state, high energy-density batteries use metallic lithium as the anode. Lithium metal is a preferred electrode material as a result of its superior thermodynamic and kinetic properties. In addition, lithium is a good conductor of electricity and heat. Furthermore, lithium's malleability and ductility make it an excellent metal with which to work. However, lithium has well-known drawbacks when used as an anode material. For example, lithium is very reactive and often creating flammability concerns.
When the battery is discharged, the anode supplies Li+ ions to the Li+ ion electrolyte and electrons to the external circuit. The cathode is typically an electronically conducting host into which Li+ ions are inserted reversibly from the electrolyte as a guest species and are charge-compensated by electrons from the external circuit. Due to the unique properties of lithium, active materials have been developed for use in lithium-ion batteries. Primary batteries or cells are those in which the chemical reaction supplying the electrons is not reversible with respect to the closed universe of the battery. A secondary battery, or cell, utilizes a reaction which can be reversed when current is applied to the battery, thus “recharging” the battery. The chemical reactions at the anode and cathode of a lithium secondary battery must be reversible. On charge, the removal of electrons from the cathode by an external field releases Li+ ions back to the electrolyte to restore the parent host structure, and the addition of electrons to the anode by the external field attracts charge-compensating Li+ ions back into the anode to restore it to its original composition.
Li—Co—O and Li—Co—Ni—O based materials are currently utilized as cathodes in lithium-ion rechargeable batteries. Although useful, lithium-ion rechargeable batteries which include Li—Co—O and Li—Co—Ni—O based materials for cathodes include a number of drawbacks. In particular, the cobalt is very expensive, and the use of cobalt and nickel results in environmental issues and thermal safety concerns.
There is therefore a need for electrode materials that have improved properties and require less expensive materials.